Method of and apparatus for compressing elastic fluids



M31227, 192sv I 1,4495%.

\ R.N.IEHRHARTI METHOD OF AND APPARATUS FOR COMPRESSING ELASTIC FLUIDS. I ORIGINAL FILED APII. 3,1919

2 SHEETS--SHEET WITNESE-BES INVENTOFI wasm.

R. N. EHRHART. METHOD OF AND APPARATUS FOR COMPRESSING ELASTIC FLUIDS.

ORIGINAL .FILED APR 3.1919.

2 SHEETS SFELT T,

INVENTUH @WMQMM WITNESSES Wm W Patented 277, i923.

RAYMOND N. EHRHART, OF IPIT'I'SBURGH, PENNSYLVANIA, ASSIGNOR TO ELLIOTT COMPANY, OLE PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYL- VANIEA.

METHOD OF AND APPARATUS FOR COMPRESSING ELASTIC FLUIDS.

Application filed April 3 1919, Serial No. 287,255. Renewed Augustaz, 1922. Serial No. 583,642.

T all whom it may concern:

Be known that l, RAYMOND N. EHR- HAn'r, residing at Pittsburgh, Allegheny County, Pennsylvania, have invented a new and useful Improvement in Methods of and Apparatus for Compressing Elastic Fluids,

of which the following is a full, clear, and" cation; Figure 4 being on the line IVIV of Figure 3;

Figure 5 is a longitudinal section showing 0 a further modification of my invent on, showing itconstructed and arranged in an annular manner;

Figure 6 is a similar view on a larger scale and showing still another modification;

Figures 7 and 8 are sections taken respectively on the lines VII-VII and YHI-VIII of Figure 6; and

Figure 9 is a transverse section. showing a modified form of nozzle.

My invention has relation to a method of and apparatus for compressing elastic fluids, and more particularly to a novel, steam ejector apparatus suitable for use as a vacuum pump for condensers, and to a novel method of operating the same.

Steam ejectors suitable for high ratios of compression, suchas are required in con nection with pumping air from steam condensers, have heretofore been made in two stages, it having been generally regarded as impossible to maintain the high vacuum required in condenser service unless such ejectors were made of at least two stages.

It has heretofore been thought impossible for a single-stage ejector to compress over the required range, but that two or more stages in series were required, each ejector of the series consisting of an inlet port, a set of 0 propelling nozzles and a diffusion structure which converts the velocity created by the propelling nozzles into increased pressure.

I have discovered that a single-stage ejec; tor can-be made which an]. operate to produce high ratios of compression and which 1s eminently suited to the same servlce to which the highly developed multistage ejectors are now' applied. it accomplish this by a certain arrangement of the propelling nozzles and diffusion structure. For maintaining such vacua as are incident to condensers serving steam turbines and the like, I find that in general it is necessary to provide such .a single-stage ejector with two nozzles or groups of nozzles, onenozzle or group handling a greater quantity of propelling fluid than the other nozzle, or group; and the first named nozzle or group projecting further into the converging element of the diffusion structure than the other nozzle or group.

where an extremely high vacuum or state of rareficat-ion is desired, as in certain branches of the chemical industry, and the like, I prefer to divide the first named or accelerating nozzles into two or more nozzles or groups of the same, each projecting a different distance into the diffusion structure,'and the sets that project furthest into the diliusionstructure passing the greater 89 amount ofprop'elling fluid. Oertainother novel proportions and arrangements of parts hereinafter described are also believed to be essential.

Referring first to that form of my inven- 35 tion shown in Figures 1 and 2, the numeral 2 designates the inlet portion of the ejector having the inlet port 3, and to which is connected the converging-diverging difi'usion structure in which 4- is the converging portion, 5 the throat, and 6 the diverging portion. 7 designates thegroup of nozzles which project farthest into the diffusion structure, and 8 the: nozzles which project to a less extent into the diffusion structure. 9 is a steam-supplying connection. In the modification shown in Figures 3 and 4, the nozzle 7* having the greatest projection is shown as having a cruciform discharge portion, the perimeter of Whose outlet is greater than that of a circle having the same cross sectional area. The other a and shorter nozzles 8 are preferably equal in-number,-to the number of lobes or wings on the non-circular ndzzle', the space between 1 .such lobes or wings acting as guides for the streams of fluid entrained hy'the shorter nozzles.

I prefer to proportion the diffuser with a slight-angle of 6 to 10 degrees, although my invention is not limited to these angles. I also prefer to use an angle of about 6 degrees in the divergence of the passages of the propelling nozzles. The nozzles which.

project farthest into the converging portion of the diffuser should pass materially-more steam than the group of nozzles which do not extend so far into the diffusion structure. For the best results, the first named nozzles should pass at least twice as much steam as is passed by the preceding set. I find that it is desirable to propdrtion the organized ejector so that the steam and entrained fluid from the first or lesser group of nozzles is delivered to the next group at relatively high velocities. In other words,

energy inefficiently, and then re-accelerated into velocity in the next stage, with further serious shock losses. I find that this conservation of velocity materially affects the efficiency of the whole mechanism, since the stream lines are not "disturbed, and the continuous flow at high velocity is conducive to high efficiencies.

In practice, a group of nozzles shoulddeliver steam to the succeeding nozzles at speeds in excess of 750 feet per second, and from this up to 2,000 feet per second.

Certain dimensions of the parts such, for

example, as the length and outlet diameter of the diverging portion of the diffuser and the size and shape of the inlet port, may vary over Wide limits, without materially influencing the efficiency of the apparatus. Certain other dimensions must, however, be within certain limits in order to obtain the desired results. For instance, the throats of the propelling-nozzles and the throat of the diffuser must bear a certain relation to each other, and the nozzle throat must be proportioned to ass an amount of steam which bears, withln certain limits, a definite relation to the area of the minimum cross sectionof the diffuser. .I also find that the effective flow area at the point where entrained fluidand motive steam from the nozzles acting on the entrained fluid is delivered to the nozzlesnext acting on the entrained fluid must be .properly proportioned; this bein due to the that the last named nozz es must receive the entrained fluid and the motive fluid from the first named nozzles at a. certain velocity. This area bears a certain relation, within limits, to the areas of the throats of the first named nozzles. r I also find that the proportioning of the impelling nozzles is a matter of great importance. The outlet areas of the nozzles compared with the areas of the minimum cross section should be much greater inthe accelerating than in the compressing nozzles, and if the accelerating nozzles be divided into two or more groups extending different distances into the diffusion structure. I find that the relation Outlet area Minimum area should decrease successively for the nozzles extending further into the difiusion structure.

For convenience in describing the proportioning of the parts, I term the first nozzles or those projecting the shortest distance into the diffuser the accelerating nozzles, and those projecting th farthest distance into the diffuser the compressing nozzles. The

-minimum cross-sectional area of the nozzles is termed the throat area, and the area at their outlet I call the outlet area. That portion of the diffuser nearest the accelerating nozzles I term the. collector; that portion immediately adjacent to the termination of the compressing nozzles, I call the mouth, and the mouth area of the diffuser, is the area of the converging tube at this point less the area taken up by the compressing nozzles. That portion of the dif- -fuser which has the smallest diameter I term the throat.

For the nozzles handling the propelling fluid, I call the relation I Qutlet ar Throat area the ratio of divergence.

Calling the aggregate areas of the acceler ating nozzle throats A, and the aggregate areas of the compressing nozzle throats B,

the mouth area C, the diffuser throat area D, and the absolute steam pressure of the motive fluid P, I find that the following relationmust be maintained for reasonable efficien y:

a. equals KD where K is a factor varying between the limits .08 and .166. b. equals QC where Q is a factor varying between the l11nits'.02 and .04. I further find that the aggregate area of the throat of the accelerinversely as the steam pressure, otherthings remaining the same.

I also find that the distancethe nozzles project into the diffusion structure bears an important relation to the etliciency of the apparatus. Calling the distance from the outlet of the compressing nozzles to the diftuser throat M, I find that for good of i'iciency the following relation must be held:

M equals Y m dia. of diil'user throat where .Y is a factor varying between the limits 2 and 2.7. Calling the distance from the outlet of the accelerating nozzles to the diffuser throat N, I find that for good ef-" ficiency the following relation must hold: 7

N equals a w dia. of difi'user throat, where Z is a factor varying between'the limits land 5.9.

I can also construct my ejector in annular formaas shown in Figure 5. The same method of proportioning area dimensions and steam flow applies to'this annular form as to the axial ejector shown in Figures 1 and 3. Figure 5 shows my ejector in an nular form. For comparison with the axial nozzles.

type of ejector, ll call the minimum distance between the sides ofthe diffuser structure the diameter of the diffuser-throat. In this figure, 1O designates the steam inlet, 11 the shorter nozzles, 12 the longer nozzles, and 13 the diii'user structure.

In Figures'6, 7 and 8, I have shown 'an-' other form of myinvention having three successive groups of nozzles 14:, 15 and 16. Each group has its nozzle connected to a header 17, having a steam-supply connec tion 18. All the nozzles discharge into the converging portion of a single diiiuser struc-- this being the equivalent of a group of a As a specific instance of an ejector emv bodying my invention and the results attained thereby, I give the following:

With an ejector havingthe aggregate throat areas of the. accelerating nozzles equal to .0197 square inches, and outlet area equal to .6 square inches, the aggregate area of the throats of the compressing nozzles equal to .098 square inches, an outlet 'areaof .88 square inches, the-mouth areas equal to .665

. square inches and the difius er throat area equal to .95 square inches, Ifind that, when supplied with steam at 115 pounds absolute pressure, it will compress 15?; pounds of the converging portion of the diffuser, the

.verging'inember of the ditlusen said nozzles within the converging portion of the difair per hour from a pressure of one inch of mercury to substantially atmospheric pressure, 43 poundsoi alr from a pressure 'of two inches absolute to substantially that of pressing an elastic fluid, which consists in utilizing the ejector action in a single stage of a plurality of jets, the rearmost :of which deliver impelled fluid at a velocity of from 750 to2000 feet per secoiid to the succeeding jets, substantially as described.

2. The herein described method of compressing an elastic'fiuid, which consists in utilizing the ejector action in a single stage of a plurality of jets from divergingpropelling nozzles, some of which e'n'tend Well into rearmost of which deliver impelled tluid-at, a velocity of from 750 to 2000 teetj per a second to the succeeding jets and-maintains? ing aismallervolume flow in veach jet 'fthan in. the succeeding jet, substantially ai's de'f scribed.

3. A single stage ejector having an inlet port through which the evacuated il uid'enter's, a converging-diverging difi'usion strue- .ture, and diverging propelling nozzles, a

'ters, a converging-diverging difi'usion structure, and diverging impelling nozzles, a. portion of which extend well within the'con havln different ratios of divergence with those aving a lesser ratio of divergence extending further into the diffusion structure, substantially as described. ,li jl 5. A single-stage ejector having an inlet ters, a converging-diverging diffusion structurc, and diverging propelling nozzles extending difierent'distances into the convergingportion of said structure, some of said nozzles being constructed to pass a greater volume of steam per unit of time than the scribed. i

6. A single-stage ejector having a converging-diverging diffusion structure, and

other of said nozzles, substantially as dotwo sets of nozzles of at least one nozzle in port through which the evacuated fluid enfuser, the nozzles of the first named set being C the mouth area ofthe diffusion structure, 5

constructed to pass a greater quantity of the steam than the nozzles of the last named set,- the last named set being constructed and arranged to deliver impelled fluid to the first named set at a velocity of from 750'to 2000 feet per second, substantially as d'e scribed.

7. The herein described method of compressing an elastic fluid which consists in utilizing the ejector action in a. single stage of a plurality of jets, the rearmost of which deliver impelled fluid at a velocity of from 1000 to 1750 feet per second to the succeed-- ing jets, substantially as described.

8. An ejector having a diffuser, and a plurality of nozzles, one of said nozzles having a plurality of wings or lobes and having its outlet nearer the smallest diameter of the diffuser than the other nozzles, said other nozzles being equal in number to and arranged'between the Wings .or lobes of the i first named nozzle, substantially as described.

' in which A represents the aggregate areas of" 9. A single-stage steam ejector comprisingadiffusion structure, accelerating nozzles and compression nozzles and in which the partsare constructed and arranged to embody the formula W equals KD,

the accelerating nozzle throats,'B the aggregate areas of the compressing nozzle throats,

D the diffuser throat area, P the absolute steam pressure of the motive fluid employed, and ,K a factor'which varies between-the limits .08 and ..16, substantially as described. 10. A single-stage steam ejector, comprising a diffusion structure, accelerating nozzles and compression nozzles, and in which the" parts are constructedand arranged to embody the formula in which A is the aggregate areas of the accelerating nozzle throats; P the absolute steam pressure of the motive fluid employed equals QC, V

and Y is a factor varying between the limits 2 and 2.7, substantially as described.

12. A. single-stage steam ejector, compris ing a diffusion'structure, accelerating and compressing nozzles, and in which the parts are constructed and arranged to embody the formula N equal Z times the diameter of the diffuser'throat, in which N is the distance from the outlet of the accelerating nozzles to the throat of the diffuser, and Z is a factor varying between the limits .4 and 5.9, substantially as described.

13. An ejector having a diffuser With a single diverging element, and a plurality of nozzles terminating at different distances from the throat of the'd ifi'user, at least some of thenozzles projecting well within the ti ally as described,

14. In a single-stage ejector, a diffuser;

structure, and at least 'two nozzles, one of 'convergingelement .of the diffuser and having different ratios of divergence, substan which projects well into the converging end of thedift'user, said last mentioned nozzle re-- ceiving fluid partially compressed within a range of from 750 to 2000 feet per second, substantially as described.

15. In a single-stage ejectorfa diffuser structure and two sets of nozzles, one of,

which sets projects well into the converging end of the diffuser, said last mentioned set of nozzles receiving fluid partially com pressed within a range of from 750 to 2000.

feet per second, substantially as described;

In testimony whereof, I have hereunto set my hand.

RAYMOND N. EHRHART. 

